The present disclosure relates to a programmable logic controller (PLC) system, and more particularly, to a PLC system that may divide memory cards in the PLC system according to a function to minimize a time taken to search the memory card.
An automation facility at the industrial site is configured by mechanical equipment including a relay, etc. In order to change the automation facility including the mechanical equipment, there is a difficulty of changing the wiring of the internal circuit of the facility. In order to overcome such a difficulty, a PLC is used.
The PLC generally performs a function similar to a computer. That is, the PLC receives a signal coming from the facility, processes the signal according to programming in the PLC and then outputs the processed signal to the facility. That is, the smoothness of the operation of the PLC means that automation facilities in the factory are efficiently operating.
FIG. 1 is a block diagram for explaining the operation of a typical PLC system.
Typically, a memory card 20 is installed in the PLC system 10 in order to be capable of mutually transmit and receive data.
A micro processing unit (MPU) 11 operates according to a set program to control the entire PLC system 10 and enables, especially, a data log module 12 and a web server module 13 to operate.
The data log module 12 performs a data log function according to the control of the MPU 11. That is, it collects a device value set in a programmable and debugging tool (PADT) and transmits the collected value to the memory card 20.
The web server module 13 performs a web server function according to the control of the MPU 11. That is, it transmits a hyper text markup language (HTML) file stored in the memory card 20 to a web browser.
A file system 14 is structured so that a search for and access to files or data in the memory card 20, data output from the data log module 12 is transmitted to the memory card 20 through the file system 14, and data transmitted from the memory card 20 is delivered to the web server module 13 through the file system 14.
The memory card 20 stores data transmitted from the PLC system 10 in a comma separated value (CSV) file and previously stores an HTML file in order to transmit a web page.
As such, the data log and the web server are functions that use the memory card, and the data log module 12 and the web server module 13 alternately accesses the memory card 20 to read data from the memory card or write data to the memory card.
In this example, when many modules access the memory card 20 to read data from the memory card or write data to the memory card, there is a limitation in that it takes a long time to search for a sector in the memory card 20.